jueves, octubre 13, 2016

One of the things that you might want to do if you are using Docker and Java is building the image from a Dockerfile in your build tool (Maven or Gradle). In this post I am going to show you how to do it in both cases.

I am going to assume that you have the de-facto project layout, having the Dockerfile file at the root of the project.

Maven

There are several Maven plugins that can be used for building a Docker image in Maven, but one of the most used is fabric8-maven-plugin.

To start you need to register and configure the plugin in pom.xml:

In configuration section you set the image name and the directory where Dockerfile is located.

Any additional files located in the dockerFileDir directory will also be added to the build context. Since Dockerfile is on the root of the project, the target directory is added too. The problem arises because this plugin uses target/docker to generate the build and if you try to build it you'll get next exception: tar file cannot include itself. To avoid this problem you need to create .maven-dockerignore file specifying which directory must be ignored at the same level as Dockerfile:

And that's all, after that you can do:

mvn package docker:build

Notice that this plugin honor Docker environment variables like DOCKER_HOST, DOCKER_CERT_PATH, ... so if your environment is correctly configured you don't need to do anything else.

Gradle

There are several Gradle plugins that can be used for building a Docker image in Gradle, but one of the most used is gradle-docker-plugin.

To start you need to register and configure the plugin in build.gradle:

In case of Gradle, you need to configure Docker host properties since plugin does not honor Docker environment variables. You need to configure them in docker {} block.

Finally you create a task of type DockerBuildImage, where you set the Dockerfile root directory using inputDir attribute and image name using tag attribute.